Significant gender differences in the prevalence of cardiovascular disease have been demonstrated. The risk of developing cardiovascular disease is considerably lower in pre-menopausal females than in age-matched males, whereas after menopause, the rate of cardiovascular disease in females rises sharply. This age- dependent reversal of female cardioprotection has been attributed to the loss of circulating female sex hormones, e.g. estrogen, in post-menopausal women. Studies in animal models also provide good evidence for direct cardioprotection by estrogen. However, clinical trials including the NIH Women's Health Initiative trial have failed to demonstrate cardioprotective benefit from hormone replacement therapy (HRT) in post- menopausal women. Resolving the current disparity requires a more complete understanding of cellular and molecular mechanisms involved in gender differences in cardioprotection. CR is the most extensively studied intervention that extends longevity and protects against stress. Our preliminary studies demonstrate that under CR, females are less tolerant to chronic catecholamine stress than males. If our findings that CR is not protective in pre-menopausal females are confirmed by this study, then understanding the molecular mechanisms mediating the adverse effects in females may shed light on those mechanisms mediating the adverse outcome of HRT therapy in post-menopausal women. There are two major hypotheses: Hypothesis A: Caloric restriction protects the heart of male mice from chronic catecholamine stress, but this is not observed in female mice. Hypothesis B: Caloric restriction induces numerous differences in gene regulation in males and females, and determining those genes that mediate the adverse effects of catecholamine stress in female caloric restricted mice may provide insight into mechanisms that are protective in the presence of pre-menopausal estrogen levels. Our study will reveal novel mechanisms of gender differences in cardioprotection in caloric restriction. The implications for Public Health are clear: understanding the cardiac protective mechanisms in caloric restricted males but not in females provide the direction for the treatment of cardiovascular disease in post-menopausal women. PUBLIC HEALTH RELEVANCE: Pre-menopausal women have reduced risk for CVD, but the rate of CVD rises sharply after menopause. The loss of circulating female sex hormones, e.g. estrogen, has been suggested to contribute to this age- dependent reversal. However, clinical trials including the NIH Women's Health Initiative trial suggest that hormone replacement therapy (HRT) is ineffective in reducing, and may actually increase CVD outcomes. The current application is to investigate the gender differences in cardioprotection in caloric restriction. We have found that the intervention of caloric restriction that extends longevity and protects against stress only protects the heart of male mice from cardiac stress, but this is not observed in female mice. Understanding the molecular mechanisms mediating the adverse effects in females may shed light on those mechanisms mediating the adverse outcome of HRT therapy in post-menopausal women and provide the direction for the treatment of CVD in post-menopausal women.